Hi Cinthia!
The default opensips.cfg file [1] also provides all commonly used cases
for t_check_trans() [2]:
* to detect and handle SIP request retransmissions
* to match hop-by-hop ACKs (i.e. ACKs to negative SIP replies, codes
3xx-6xx). These ACKs are not routed per se -- rather OpenSIPS processes
them but generates its own version of the ACK when replying upstream, so
the script handling is different.
* to test if a CANCEL actually matches an INVITE. If it doesn't, you'd
probably want to drop it.
To conclude: it's fine to call t_check_trans() right at the top of the
script. Make sure you save the return code for later use inside the
has_totag() block (mid-dialog requests).
Best regards,
[1]: https://github.com/OpenSIPS/opensips/blob/master/etc/opensips.cfg
[2]: https://opensips.org/html/docs/modules/3.0.x/tm.html#func_t_check_trans
Liviu Chircu
OpenSIPS Developer
http://www.opensips-solutions.com
On 12.09.2018 19:50, Cinthia Leung wrote:
Hi all!
Traditionally t_check_trans() is used in the "new requests" and
specific part of the in-dialog section. I wonder if it's OK to put it
right at the top most of the script. Thanks.
Cindy
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